This invention relates to test systems and, in particular, to a system for assuring that a device under test is properly acoustically coupled to a test fixture prior to the execution of the acoustic tests by the test fixture on the device under test.
It is a problem in the field of acoustic testing of a device to ensure the proper acoustic coupling of the device under test to the test fixture. In particular, a device under test typically undergoes a plurality of tests to ensure its proper operation as part of the device manufacturing process. Where the manufactured device includes acoustic elements, the response of these acoustic elements to predetermined test inputs are measured to guarantee proper operation of these acoustic elements.
For example, in the case of telephone handsets, the handset includes an earpiece and a mouthpiece, that are equipped with a handset receiver and a handset transmitter, respectively. The handset transmitter is responsive to the presence of a user""s voice to generate electrical signals that correspond to the user""s voice, for transmission over the telephone network to a destination telephone set. Similarly, the telephone handset includes handset receiver located in the earpiece to receive the transmitted electrical signals corresponding to a calling party""s voice signals and produce an audio output that accurately reproduces the calling party""s voice input. To test the operation of the handset transmitter and receiver contained in the telephone handset mouthpiece and earpiece, respectively, a set of industry-standard tests are executed on the device under test. Typical test definitions can be found in the publications xe2x80x9cIEEE Standard Method for Measuring Transmission Performance of Telephone Setsxe2x80x9d and xe2x80x9cIEEE Standard Method of Determining Objective Loudness Ratings of Telephone Connections.xe2x80x9d These publications document standardized tests that are preformed on telephone handsets to verify their operational capabilities.
To implement the tests that are defined in the above-noted publications, test fixtures have been designed to enable the telephone handset to be mounted thereon, to receive test signals and measure audio signals output by the telephone handset. The test fixtures of necessity entail mounting the device under test to the test fixture via an acoustic coupler that places the earpiece of the telephone handset in close proximity to an audio detector in the test fixture that functions to measure the audio output of the telephone handset in response to the application of standardized test signals thereto. However, a problem with existing test fixtures is that it is difficult to ensure the consistent mounting of a telephone handset in the acoustic coupler that is part of the test fixture. The mounting of the telephone handset is a function of the accuracy of the operator who is running the test. If the telephone handset is not accurately mounted in the acoustic coupler, the test results are inaccurate. In a worst case situation, where the mounting of the telephone handset is grossly misaligned with the acoustic coupler, the telephone handset can fail the test, thereby necessitating the remounting of the handset and reexecution of the test to determine whether the test failure was a result of operator error of true failure of the telephone handset. In addition, the test results obtained from existing test fixtures vary widely and it is difficult to obtain an accurate representation of the true audio response of the telephone handset to the applied test signals due to the audio coupling limitations introduced by the acoustic coupler. Therefore, existing test fixtures simply identify gross anomalies, and produce a simple pass/fail response rather than producing accurate representations of telephone handset performance.
The above described problems are solved and a technical advance achieved by the present system for assuring proper acoustic connection of a device under test to a test fixture, which generates an audible test signal external to the telephone handset-acoustic coupler interconnection to test the efficacy of the coupling of the telephone handset to the acoustic coupler of the test fixture. In particular, when the telephone handset is mounted in the acoustic coupler of the test fixture, this acoustic coupling should substantially block all audio signals that are present external to the acoustic coupler-telephone handset interconnection, from reaching the audio detector that is located in the acoustic coupler of the test fixture. Failure to substantially block the external audio signals indicates the inefficient mounting of the telephone handset in the test fixture.
To determine whether the telephone handset is properly mounted in the acoustic coupler, the system for assuring proper acoustic connection of a device under test to a test fixture generates a test signal of audio frequency outside the bandwidth of the telephone handset and outputs this audio test signal proximate the telephone handset when it is mounted in the test fixture and external to the acoustic coupler-telephone handset interconnection. If the test signal is detected by the audio detector that is mounted in the acoustic coupler, then it is indicative of improper mounting of the telephone handset in the test fixture. Furthermore, the magnitude of the detected test signal is indicative of the degree of audio leakage into the acoustic coupler-telephone handset interconnection and this information can be used to adjust the results of the test process if the telephone handset interconnection is adequate for test purposes, but not optimal. Once the test signal is applied and the output of the audio detector measured, the test process can continue.